Interferometric waveguide modulators famed by Ti diffusion in LiNb03 are under development for use in a high-speed electrooptic analog-to-digital (A/D) converter operating in the 6-bit 1-GS/sec range. The operational principles of these modulators and the design considerations for the A/D converter will be reviewed and the operational characteristics of the fabricated waveguide modulators will be described. The devices have a 17-dB extinction ratio and modulation at 1.4 GHz has been demonstrated. To simulate the A/D conversion application, the modulators have also been used in conjunction with a frequency-doubled mode-locked Nd:YAG laser to sample a 69-MHz signal at 275 MS/sec.